Manufacture of screws with a self-cutting thread



Feb. 18, 1941.

J. MEERSTEINER -MANHFACTHRE OF SCREWS WITH A SELF-CUTTING THREAD Original Filed July 17, 1936 INVENTOR ATTO RNEYs thread with thread-forming elements.

Patented Feb. 18, 1941 UNITED STATES MANUFACTURE OF SCREWS WITH A SELF-CUTTING THREAD Johann Meersteiner, North Bergen, N. J., assignor, by mesne assignments, of one-half to Paul Bechert, Saaz, Czechoslovakia; Frieda Meersteincr administratrix of said Johann Meersteiner, deceased Continuation of application Serial No. 91,085, July 17, 1936. This application February 23, 1937, Serial No. 127,266. In Czechoslovakia February 22, 1936 16 Claims.

(Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G. 5)

This application is a convention application (filed in Czechoslovakia February 22, 1936) and a continuation of application Serial No. 91,085 filed July 17, 1936, for which it is substituted.

The invention relates to the rolling of selftapping screws, bolts, etc. in a wide variety of forms.

The rolling of bolts for the purpose of producing screws with a self-cutting thread is known. Hitherto it has been proposed to produce the longitudinal grooves in the bolts which interrupt the turns of the screw threads in screws of this character by allowing rolling elements to act on the finished screw thread turns. The disadvantage of this is that the finished screw thread turns are subjected to excessive stresses by the rolling elements forming grooves so that an unexpected, unpredictable and undesirable flowing of the metal present in the screw-thread turns results, which prevents a perfect final product from being obtained. A like disadvantage has also been encountered where both dies have thread-forming elements on their working faces, one of said dies having also ribs extending across the angular thread-forming ridges milled out on the face of the die and incorporated with the said ridges in the working face of the die. The jolting, jamming and crowding action which occurs under these circumstances causes upset of the metal. This tends to prevent the true thread outline from being produced.

Heretofore in rolling self-tapping screws, it has been considered essential to provide each of the dies of the pair designed to produce the interrupted This required the dies to be maintained in precisely correct relation since the slightest deviation would cause the thread-forming elements of the respective dies to work against each other and injure the thread intended to be produced by the exact cooperation of both. I have found, however, that the idea that both dies must be provided with thread-forming elements for forming the same thread is erroneous, and that, on the contrary, self-tapping threads are produced on screws with greater accuracy if only one rollingdie is provided with the threading face and the other rolling die is provided exclusively with groove forming elements for producing the thread-cutting interruptions therein. Thus, allocating the threadforming elements to one die only and the groove or etc. forming elements which produce the thread-cutting, i. e. self-tapping, edges of the thread only to the other obviates the necessity for exercising this care and insures precision in the threads and grooves unattainable by other methods of rolling.

Ihe existence of old patents for knurling and for roughened nails, such as the patent to George F. Simonds, Device for knurling the surfaces of metal articles No. 446,933 dated February 24, 1891 and the patent to W. C. Lipe for Nail, No. 510,035, December 5, 1893, in which different elements are allocated to the respective dies, is noted as in no wise inconsistent with the foregoing statements, the purpose and nature of the subject matter of these patents being quite difierent from the present invention and both being incapable of producing self-tapping screws.

In one aspect the invention consists in the fact that in the rolling of the bolt a continuous crossing of the diverse rolling elements, 1. e. threadforming and the thread interrupting groove-forming and self-tapping edge producing elements takes place, that is to say, the deepening action of the rolling elements forming grooves increases in proportion as the deepening action of the rolling elements forming the screw-thread progresses and, in contrast with what happens in previously known methods, the metal is but little stressed. The production of the thread by this rolling process is accompanied by the simultaneous progressiveformation of the grooves which interrupt the thread and give the screw its self-tapping action by providing it with cutting edges. The result obtained in comparison with what is already known is that only a considerably diminished amount of material is coused to flow in each case and this operation is therefore rendered incapable of affecting the material in such a way as would adversely act upon the final form of the self-cutting screw-thread.

The practice of drilling smooth faced bores (of about the diameter of the body of the screw or a little larger) in soft iron and soft steel and of introducing thereinto drive pins or screws which themselves out threads or other grooves in the face of the bore is known, and the method of rolling herein described produces pins and selftapping screws to be used in this way, and in both cases produces cutting edges capable of cutting the metals named as well as other and softer materials, in which suitable holes have been drilled, but not threaded in advance of pin or screw insertion. The words self-cutting threadj as used in the specification and claims imply this capability.

The machine by which this process is carried out is characterized by giving only one of the rolling dies the cross-sectional profile of the thread grounds between the ribs (see Fig. 1).

and by giving the other only the developed counterpart of the interruptions of the threads which have to be formed thereon. One Jaw thus has the set of die elements for forming the main thread pattern, the other the set of die elements for forming the interruptions in the main thread pattern by which the screw is given the cutting edges which make it self-tapping.

In the drawing which illustrates" one apparatus suitable for carrying out the process, Fig. 1 is a side elevation of so much of a conventional dierolling machine as is necessary to illustrate diagrammatically the relation of the dies thereon and the operation.

Fig. 2 is a perspective view of a novel pair of dies showing their characteristics discussed above. While the method may be preformed with different types of die-rolling apparatus modified in accordance with this invention, the machine shown in Fig. 1 is suitable for carrying it out. In this figure, I indicates the thread-forming die which in the illustrated machine is fixed and with respect to which the grooveforming die 2 reciprocates as indicated by the arrows, a driven shaft and suitable connections, not shown, being provided for that purpose. The thread forming elements 3 which are milled into, or otherwise provided on, the working face of the die I, are close set and extend generally longitudinally of the die face at a small angle, as shown in the drawing, to form on the headed screw blank (Fig. 1) an encompassing thread of low pitch as usual in screws of this type. The die I is usual in character and varies according to the nature of the thread to be rolled. Since the screw can be applied by turning it in, the thread is aptly termed a turn-in thread. This die is, however, the only main thread-forming die. The groove-forming elements 4, relatively large and widely spaced as compared with the threading ribs 3, and which are preferably inclined forward as shown, are milled into the working face of the die 2, the working face of each die having only its special stated kind of elements.

It will be clear that to avoid the otherwise inevitable duiling of the thread edges being produced, the elements 4, which in the illustrated die are continuous ribs extending completely across the face of the die 2, are made of greater height (by say 20 or 3 per cent) than the depth of the grooves of the thread-forming elements 3, so that in the rolling of the screws the portions of the reciprocating diewhich come in contact with the blank being threaded are the elements 4, the blanks, and in particular the sharp edges of their threads, not contacting at all with the The ribs 4 acting in turn thus control and determine the indenting effect of the threading faces or elements of the other die as each rib produces its own indenting effect, the formation of the grooves and the threading being thus coordinated and the depth of both the thread and the grooves progressively increasing during the forward movement of die 2.

It will be understood that the number, spacing and inclination of the ribs as well as their cross section are varied according to the nature and size of the screw or bolt to be formed, the number of its grooves or interruptions, etc., and that various threads and thread interruptions may be produced in this way.

What is claimed is: l

1. The method of forming a self-tapping screw 1 which consists in rolling grooves into a blank to form an encompassing thread and simultaneously progressively rolling generally longitudinal grooves into such blank to interrupt the encompassing thread, the thread-rolling process taking place between dies only one of which has a thread producing work face.

2. The method of forming a self-tapping screw which consists in rolling grooves into a blank to form an encompassing thread of low pitch and simultaneously progressively rolling generally longitudinal grooves into such blank to interrupt the encompassing thread and provide it at each interruption with a generally transversecutting edge, the thread-rolling process taking place between dies only one of which has an encompassingthread-producing work face.

3. The method of manufacturing self-tapping threaded articles having an encompassing selfcutting screw thread comprising rolling the blank between dies only one of which is a screw-threading die having a working face profile corresponding to a developed counterpart of the thread around the screw and the other of which is a grooving die having groove-forming elements corresponding to the interruptions to be rolled in the thread.

4. In a machine for rolling self-tapping threaded articles, a thread-rolling die and a thread-grooving die constituting a pair of rolling dies between which the blank is rolled in threading and grooving it, the grooving die having only grooving elements and the threading die having only threading elements.

5. A machine for making self-tapping threaded articles having an encompassing thread interrupted at a plurality of spaced points comprising a thread-rolling die having a working face corresponding to a developed counterpart of the thread around the screw and a rolling die constituting with the first named die a pair and having its working face given' a profile corresponding to the developed counterpart of the spaced interruptions to be rolled in the thread and devoid of thread rolling elements, and means for giving said dies relative movement to roll the screw.

6. A process for the manufacture of self-tapping articles having an interrupted self-cutting thread by means of rolling dies wherein the rolling both of the entire thread and of interruptions therein is carried out exclusively by a continual crossing of thread-forming and interruption-forming rolling elements on respective opposed dies, the deepening action of the rolling elements of one of said types, i. e. respectively thread-fuming and interruption-forming, being progressive and being proportioned to the deepening action of the rolling elements of the other of said types, and the interruption-forming elements providing thread interruptions with self-tapping edges.

7. The method of making a screw provided with self-tapping thread interrupted by grooves extending generally transverse of the thread consisting in rolling, exclusively at opposite sides of the blank, respectively, the thread and the transverse grooves interrupting the thread.

8. The method of making a self-tapping screw consisting in rolling the part of a blank to be provided with interrupted self-tapping thread between dies only one of which has thread-forming elements, and the other of which has grooveforming elements.

9. In a machine for rolling self-tapping screws a pair of dies, one of the dies having its working face clothed with a set of closely set thread-forming ribs extending generally lengthwise of the die at a slight angle and the other having, throughout substantially its entire length, parallel widely spaced ribs of greater height than the depth of the grooves in the other die and extending completely across the die face and inclined toward the front end of the die.

10. The method of forming a self-tapping screw which consists in rolling a blank between two dies or platens, one die or platen, only, having screw-forming threads and the other die or platen having groove-forming ribs so that progressively with the rolling of the threads on the blank grooves interrupting the threads and providing it with self-tapping cutting edges are simultaneously rolled into such blank.

11. A rolling machine for the production of selftapping screws characterized in that the pair of rolling dies or platens has one die or platen, only, having screw-forming threads while the working surface of the other die or platen has a profile corresponding to the developed counterpart of the interruptions of the thread which are to be made at spaced intervals around the circumference of the screw so that the rolling of the grooves into the blank to form a thread is constantly accompanied by a simultaneous progressive rolling of other grooves into such blank to interrupt the thread.

12. A screw having a self-cutting encompassing thread produced by rolling grooves into a blank to form said thread and simultaneously progressively rolling generally longitudinal grooves into the blank to interrupt this encompassing thread and form in it self-cutting edges at thread interruptions, the rolling of the interrupted blank-encompassing thread taking place between-die face portions only one of which has the thread producing work face.

- 13. The method of making a sen-tannins screw consisting in rolling on a headed screw-blank at one side only of the blank a blank-encompassing turn-in thread of low pitch, and, while the thread is being progressively formed at that side of the blank, providing the thread at intervals around the blank with cutting edges generally transverse of the thread by transversely grooving or notching it gradually at the opposite side of the blank as the thread is taking shape, thereby giving the screw a turn-in threadloi self-tapping character.

14. A screw having a self-cutting thread produced by rolling grooves into a blank to form said thread and simultaneously progressively rolling generally longitudinal grooves into the blank to interrupt this thread, the thread rolling process taking place between dies only one of which has the thread producing work face.

15. A process for the manufacture of self-tapping articles having an interrupted self-cutting thread by means of rolling dies wherein the blank 'is kept rolling exclusively by opposed respectively threading and grooving dies and the rolling of all the thread and of interruptions therein is carried out by a continual crossing of thread-forming and groove-forming rolling elements on respective dies, the deepening action of the rolling elements of one of said types being progressive and being proportioned to the deepening action of the rolling elements of the other of said types, and the groove-forming elements providing the thread with groove-bounding self-tapping edges.

16. The method of making a self-tapping screw consisting in rolling into a blank, thread and longitudinal grooves interrupting the thread and making the screw self-tapping, and keeping the blank rolling during this operation exclusively by grooving ribs on one die and by threading ribs on the other.

JOHANN MEERSTEHNER. 

